1. Field of the Invention
A filter surface specifically configured for use with a filter pan in the separation of liquids from solids such as the separation of phosphoric acid from phosphoric slurry.
2. Description of the Prior Art
A number of filtering apparatus comprising a large horizontal filter medium for use in the production of phosphoric acid and treatment of metal ores have been developed.
Typically a pan is disposed below the filter medium to receive the filtrate. Vacuum is applied to the pan. Slurry is fed to the upper surface of the horizontal medium. Gravity and the pressure of the atmosphere cause the filtrate to pass through the medium. Solids, which are retained by the pore size of the filter medium, deposit on the upper surface, are periodically air dried and then removed either by inverting the filter or by scraping.
U S. Pat. No. 3,139,404 relates to large horizontal rotary filter structure. As disclosed a multiplicity of filter cells, each comprising a pan and a horizontally disposed filter medium, are supported in circular array for charging, draining, and washing. Each cell is overturned at the end of each filtering cycle for discharge of filter cake. The rotary filter includes the pivotal cell filter in which each cell is mounted for pivotal inversion about an axis which extends generally radially from the center of the numerous stations past which cells rotate, and inversion and return of the cells is easily effected as with a controlling cam track.
The filter medium is typically interwoven monofilament made of polypropylene, polyethylene with some very few made of polyester. The woven cloth is supported by ribs or perforated plate to withstand the filter cake weight and effect of the vacuum.
Embedding of crystals within the cloth, tilting the pans, as described above, and intensity of washing severly limit the life of the cloth. Typical cloth life is two to three weeks before replacement.
U.S. Pat. No. 4,391,706 discloses a filter element sealing device with a metal plate and sealing strip to secure the filter cloth to the filter pan.
U.S. Pat. No. 3,491,886 relates to a polygonal filter sector with filter media or filter cloth overlaying each sector face secured in place by a stretcher frame for holding the media, or filter cloth taut over the panels.
U.S. Pat. No. 1,860,937 describes an improved means for securing filter media in a disc filter to permit more easily replacing and renewing filter leaves.
In all the above prior art, attempts have been made to improve the arrangement of holding the filter media, or filter cloth to promote rapid cloth changing or improve filter cloth life.
The present invention seeks to provide a simple means to facilitate the separation of a liquid such as phosphoric acid from calcium sulfate by eliminating the use of filter media or filter cloth by replacing both the filter cloth and support grid with a profiled metal surface which does not require frequent renewal and may be cleaned by washing without removal from the filter structure.
Other examples of the proir art are: U.S. Pat. Nos. 24,150; 3,139,404; 3,216,567; 3,216,576; 3,426,909.